Control flow and arrays

Make the loop's state explicit

Conditions require boolean expressions; Java does not convert numbers or references to truth values. && and || short-circuit, so a guard can protect a dereference or array access. & and | on booleans evaluate both sides. switch expressions yield a value and must cover every possible input through cases or a default; statements can still be useful when dispatch performs effects.

String text = null;
boolean nonempty = text != null && !text.isEmpty();
assert !nonempty;

A useful loop invariant describes the prefix already processed. In a scan for contiguous runs, the active start is either absent or the beginning of a run whose every element satisfies the predicate. End that run once when the predicate fails, then handle a final run at the array boundary. Treating boundaries as half-open [start,end) makes run length end-start and allows end==array.length.

Arrays and ownership

Arrays have fixed length and reified component types; primitive arrays store primitives without boxing. ArrayList grows and stores references. An enhanced for loop gives values, so assigning its loop variable does not replace an array cell. Use an index loop when position is part of the result. Arrays.copyOf or clone copies a one-dimensional primitive array; copying an array of object references does not clone those objects.

long[] original = {3, 5};
long[] snapshot = original.clone();
snapshot[0] = 99;
assert original[0] == 3;

Array bounds failures are exceptions, not sentinel values. A common off-by-one bug reads values[end] after the last valid index. Another records a run at every matching element, producing overlapping fragments instead of maximal runs. Prefer a small amount of explicit state over flags that can contradict one another. A single scan should cost O(n) with workspace proportional to returned runs.